The Lord of the Rings, Appendix A, Annals of the Kings and Rulers: Gondor and the Heirs of Anárion

The rebels of Umbar had never ceased to make war on Gondor since the death of Kastamir,1 attacking its ships and raiding its coast at every opportunity. They had however become much mixed in blood through admission of Men of Harad, and only their chieftains, descendants of Kastamir, were of Númenórean race. Learning through spies that Minardil was at Pelargir, suspecting no peril since the crushing of Harad and Umbar by his father, Angomaite1 and Sangahyanda,1 leaders of the Corsairs of Umbar, great-grandsons of Kastamir, made a raid up Anduin, slew the king, ravaged Pelargir and the coasts, and escaped with great booty.

The Peoples of Middle-earth, HoME Vol 12, Part 1, Ch 7, The Heirs of Elendil: The Southern Line of Gondor: The Anárioni